The present invention relates generally to woodworking tools and more particularly to a doweling jig. A common way to join together two pieces of wood is to drill two holes, one hole in each of the facing surfaces of the two pieces of wood, and to glue a length of a wooden rod, called a dowel, into both holes with the surfaces of the wood contacting one another. This technique is called doweling. For example, doweling is widely used for joining together the various wood parts of a door. A series of dowels hold the rails of a door to its stiles. Typically, the dowels are spaced 1.260 inches apart in the United States standards and 32 millimeters apart in metric system countries.
Successful doweling requires precision in the sizing of the holes and dowels as well as precision in the alignment of the holes so that corresponding holes will line up correctly in the two pieces of wood to be joined. The holes must be drilled at the correct location and at the correct angle in the wood. Drilling the holes with sufficient precision by hand is practically impossible. Therefore, tools have been employed to help locate and align drills during doweling. Large and elaborate automatic machinery is available which can be programmed to precisely drill the dowel holes. However, such machinery is too expensive and/or otherwise impractical for many applications such as home workshop doweling or small scale commercial doweling operations. Smaller hand tools are also available for locating and drilling dowel holes. These tools are referred to as doweling jigs.
When using doweling jigs it is important to be able to position the jig accurately relative to locating marks made on the wood. One common way of marking two pieces of wood to be joined is to position the two pieces as they are desired to be positioned after the doweling process is completed. Then a mark is made across the surface of the two pieces to cross the interface of the two pieces of wood at the desired location of the dowel. The desired locations are chosen to give sufficient strength to the particular size and type of wood being joined. Some prior types of doweling jigs cover the marks making proper positioning of the doweling jig different without drawing subsequent marks on the surface to be drilled. Additional marking requires significantly additional time and introduces further error into the process.
A variety of different types of doweling jigs are known. To use some types of doweling jigs the width of the workpiece is measured by hand and the doweling jig is adjusted by hand to half the measured distance to center the jig on the workpiece. The drill is inserted through a guide bushing held by the jig and is guided into the workpiece at the proper angle by the bushing. The process is repeated for additional holes on the workpiece and on the mating workpiece. The disadvantage of such jigs is that the thickness of the workpiece must be measured and the jig adjusted by hand accordingly to assure that the bushings are centered on the workpiece. The measuring process is time consuming and prone to error. Inaccurate measuring results in misalignment of the two workpieces when joined or may require filling a misplaced hole and redrilling. In addition, this type of jig when attached to the workpiece blocks the operator's view of the marks on the workpiece as mentioned above.
Another type of doweling jig automatically centers the dowel holes in the wood workpiece. One known example is a hand-held doweling jig with a bushing centered between two posts. The bushing is centered over the edge of the workpiece by placing the jig upon the surface of the workpiece so that the posts extend down along the sides of the workpiece. The operator then rotates the doweling jig until the posts firmly grip the sides of the workpiece thereby centering the bushing upon the edge of the workpiece. However, this doweling jig does not allow for a plurality of dowel holes to be made with one setting and cannot be aligned with the marks on the workpiece.
Another example of an automatically centering doweling jig has two opposed vice plates with a center bar mounted in between. A threaded tightening bolt brings both plates toward the center bar at the same rate. Thus, the center bar remains centered over the edge upon tightening the plates. In this type, multiple holes may be provided through the center bar. Again, the wood marks are not visible with this type of clamp making alignment difficult. Additionally, because the bolt extends through a wide portion of the middle of the center bar, no drill guide can be located there.
In yet another exampled of a self centering doweling jig described in U.S. Pat. No. 2,810,310, two side plates are held to the sides of the wood by a clamp. The side plates are pivotally connected by a bridging bar. A hub is positioned at the center of the bridging bar between pivot points on the side plates. Thus, when the side plates are clamped to the workpiece the hub hole is centered over the workpiece. This device, too, blocks the marks on the wood and requires readjusting for each hole drilled.
There is a need in the art for doweling jig which is automatically centered upon the workpiece, enables equal spacing for a number of bushing holes and allows the user a clear view of the measuring marks on the workpiece.